Tuesday, August 10, 2010

Great “How to …”

If you’re new to machine vision you’ll find lots of articles and papers on the web about lighting but precious little on actually developing an inspection application. But fortunately Ben Dawson of Dalsa has a piece in the July 2010 Control Engineering magazine intended to help correct that problem.

In “How To Inspect Closures With Machine Vision” Ben compares and contrasts the merits of template matching with feature extraction. (“Feature extraction” might be better thought of as making measurements on an image.)

While the piece is about inspecting plastic bottle caps it’s the detail on the two approaches that is really useful. In particular, Ben does note that template matching has its weaknesses.

My view is that while template matching – subtraction from a golden template, if you will – is attractive to the newbie, it’s not really terribly robust. In many situations a feature extraction approach will give you a more robust solution.